Conventionally, as one mode of a tractor, there has been known a tractor which supplies outside air purified through a pre-cleaner to an engine after further purifying the outside air through an air cleaner (for example, see patent literature 1).
Further, while the engine and the air cleaner are covered with the open able bonnet, the pre-cleaner is arranged outside and above the bonnet. Accordingly, it is possible to view a dust-collection/storage state of the pre-cleaner easily.
However, when the bonnet is opened, the pre-cleaner which is arranged above the bonnet becomes an obstacle and hence, it is necessary to preliminarily remove the pre-cleaner or a portion of an intake pipe connected to the pre-cleaner thus giving rise to a drawback that such a removal operation takes time and efforts.
Further, in a desert area or an area with a large amount of yellow sands, it is necessary to frequently perform maintenance of the pre-cleaner thus giving rise to a drawback that such maintenance requires considerable amounts of times efforts.
To overcome the above-mentioned drawbacks, a tractor which arranges a pre-cleaner in the inside of a bonnet is developed (for example, see patent document 2).
Here, while a pre-cleaner is arranged in front of a radiator, an air cleaner is arranged behind the radiator.
However, the above-mentioned latter tractor still has following drawbacks.
(1) The pre-cleaner is arranged in the inside of the bonnet and hence, to view a dust-collection/storage state of the pre-cleaner, it is necessary to open the bonnet every time for viewing the dust-collection/storage state of the pre-cleaner thus giving rise to a drawback that such an operation requires times and efforts.
(2) The air cleaner is arranged behind the radiator and hence, there exists a drawback that a communication pipe which connects the pre-cleaner arranged in front of the radiator and the air cleaner is elongated and, at the same time, the pre-cleaner and an air tank cannot be arranged in a compact manner.
(3) The air cleaner is arranged behind the radiator and hence, the air cleaner is heated by heat radiated from the radiator thus elevating a temperature of the outside air which is purified through the air cleaner. As a result, high-temperature air is supplied to an engine thus giving rise to a drawback that an output of the engine is lowered.
Patent document 1: JP-A-2004-299635
Patent document 2: JP-UM-B-7-38649